36 MORPHOLOGY AND EVOLUTION
whilst others are willen; and their vocal powers vary from a sharp squeak to loud howlings, which have earned for their producers the popular name of " Howler Monkeys." Most species are natives of Brazil.
Nostrils and Septum Nasi (fig. 7).—Although the Hapalicte and Cebidae are all included in the Platyr-rhine section the nasal septum is not always broad.
FIG. 7.—The Brown Capuchin (Cebits fatuellutt).
H. 0. Forbes has shown that the septum is comparatively narrow in Aotus, Alouatta and Brachyteles, and the nostrils are directed more forwards than in all other genera which have the typical broad septum and outwardly-directed nostrils. The nostrils are circular, slit-like or S-shaped. The septum and nostrils in the primitive Douroucoulis are like those of the Lemur-oidea, and different from those of all other Primates.